With conventional internal combustion engines, power is derived from the combustion of air and fuel (e.g., gasoline and air) resulting from the ignition of a highly compressed air-fuel mixture contained within one or more combustion chambers. In a typical internal combustion engine, the inward motion of a reciprocating piston within a cylinder compresses the air-fuel mixture for ignition and combustion. The expanding gases resulting from combustion impart a tremendous force against the piston and drive it outwardly within the cylinder. The piston is typically linked to a crankshaft in a manner such that linear reciprocating motion of the piston is converted into rotational motion of a drive shaft.
A typical sequence of operation of a combustion engine includes delivery of the air and fuel into the combustion cylinder, compression of the air-fuel mixture within the cylinder by the piston, combustion of the mixture which powers the piston and crankshaft, and then exhaust of the "spent" fuel mixture from the cylinder. Repeated performance of these steps results in the continuous delivery of power to the crankshaft which, in turn, can be used to do the desired work, such as propel a motorized vehicle.
Internal combustion engines employing reciprocating pistons may be categorized as "two-stroke" or "four-stroke" engines. The two-stroke cycle engine completes the four steps of the power producing cycle; i.e., fuel intake, compression, power, and exhaust of the spent fuel mixture, during a single reciprocation of the piston (and one resulting revolution of the crankshaft). In contrast, a four-stroke engine requires two revolutions of the crankshaft for a power producing cycle and, thus, two upward and downward strokes of the piston to complete the intake, compression, power, and exhaust steps.
Two-stroke engines typically pre-mix the air and fuel before delivery into the cylinder. The air-fuel mixture is then delivered and the spent combustion gases are exhausted from the cylinder when the reciprocating piston exposes intake and exhaust ports, respectively, in the cylinder walls. Often the piston exposes both the intake and exhaust ports simultaneously, allowing the fresh fuel mixture to purge the cylinder of the exhaust gases. In contrast, the four-stroke engine typically delivers the fuel only after the spent gases have been exhausted and the fuel is frequently delivered into the cylinder separately from the incoming air. Control of the incoming air and exhaust of the spent gases in most four-stroke engines is achieved with an array of mechanically linked intake and exhaust valves.
Two-stroke engines offer certain advantages over four-stroke engines because the former produces power strokes twice as often as compared to the four-stroke engine. This permits two-stroke engines to be smaller in size and lighter in weight than four-stroke engines with a comparable power output. Two-stroke engines are also less expensive to manufacture and build because they require fewer parts that are subject to wear, breakdown and replacement. Two-stroke engines also dispense with the need for a complicated intake and exhaust valve structure.
Two-stroke engines, however, are generally not as efficient as four-stroke engines because two-stroke engines do not effectively remove all of the exhaust gases from the combustion chamber before the next power producing cycle. In a typical two-stroke engine, both the intake port and the exhaust port are open at the same time to enable the new air-fuel mixture to flow into the combustion chamber and to allow the escape of the exhaust gases. The concurrent opening of the intake and exhaust ports allows the fresh air-fuel mixture to purge the exhaust gases out of the combustion chamber through the exhaust port. This is disadvantageous because some of the fresh air-fuel mixture escapes through the exhaust port reducing engine efficiency by failing to utilize all of the fresh air-fuel mixture during the combination process. In addition, some of the exhaust gases mix with the incoming fresh air-fuel mixture which further reduces engine efficiency because noncombustible gases remain in the combustion chamber during the subsequent power cycle.
Efforts to improve the removal of the exhaust gases from the combustion chamber have focused primarily on the development of improved scavenging or removal of the exhaust gases by positively pumping the fresh air-fuel mixture into the combustion chamber. As known in the art, one method uses the changing volume of the crankcase (which changes with the reciprocating movement of the piston) to pressurize the incoming air to help force the exhaust gases out of the cylinder. This approach leads to considerable complexity in crankcase design, requires additional working components, creates sealing and lubrication problems, and adds to the cost of manufacturing, operation and maintenance.
Another known method to improve removal of the exhaust gases from the combustion chamber is to use devices such as a supercharger to force the air-fuel mixture into the cylinder. This subject is discussed at length in the September 1992 issue of Popular Mechanics at page 33. Superchargers comprise a pump that increases the pressure of the air-fuel mixture entering the cylinder. Superchargers generally include a blower that is driven by a belt, gear or chain that is connected to the drive shaft of the engine. However, superchargers include serious disadvantages such as increased weight, added complexity, reliability handicaps, and maintenance problems.
Conventional internal combustion engines also lose power and efficiency because the reciprocating piston is attached to the crankshaft by a connecting rod and a wrist pin to translate linear reciprocating motion of the piston into rotational movement of the crankshaft. The use of the connecting rod and wrist pin results in uneven and excessive wear to the piston and cylinder wall because lateral forces are transmitted through the connecting rod in directions other than through the centerline of the piston. In a typical engine, the cylinders are held stationary in the engine block and the pistons are connected to the rotating crankshaft by the connecting rod which pivots about the wrist pin. When the piston is in any position other than the top dead center or bottom dead center of the cylinder, the force acting through the centerline of the piston is not aligned with the axis of rotation of the crankshaft. Transverse or lateral force vectors, which cause uneven wear of the piston, are created because the force is not acting directly upon the crankshaft.
This disadvantage is overcome by using oscillating cylinders that rotate about a set of trunnions so that the centerline of the piston is at all times aligned with the crank throw of the crankshaft to eliminate the lateral force vectors. The oscillating cylinder engine uses a piston rod that directly connects the piston to the crankshaft to eliminate the need for the wrist pin and connecting rod. The trunnions enable the cylinders to oscillate back and forth across a small arc while tracking the rotational movement of the point of contact between the base of the piston rod and the crankshaft. The rigid, fixed-length piston rod connecting the piston to the crankshaft causes the cylinder to oscillate while the piston rotates semi-elliptical in their motion to turn the crankshaft.
Oscillating cylinder engines of old required a complicated maze of passageways and connections to direct the air-fuel mixture and exhaust gases through the engine. For example, U.S. Pat. No. 878,578 issued to Thompson discloses an engine with two oscillating cylinders. The cylinders are connected by four different passageways to control the flow of the air-fuel mixture into each cylinder and the removal of the exhaust gases from each cylinder. These passageways create a complicated system that is difficult to manufacture and expensive to assemble. U.S. Pat. No. 1,135,365 issued to Dock and U.S. Pat. No. 1,877,760 issued to Berner disclose oscillating cylinder internal combustion engines where the rocking motion created by the oscillating cylinder requires a complex series of chambers, passageways and apertures to regulate the flow of the fuel mixture and exhaust gases through the engine. Thus, prior oscillating cylinder engines required a plurality of passageways and interconnects to control the flow of the air-fuel mixture and exhaust of the spent gases from the combustion chamber.
As shown in my earlier U.S. Pat. No. 5,275,134, I disclosed an internal combustion engine with adjacent air and power cylinders that oscillate about two sets of adjoining co-axial trunnions. The trunnions eliminate the complicated tubing and passageways required to control the flow of the incoming air-fuel mixture and exhaust of the spent gases through the engine because the hollow trunnions periodically align openings or apertures in the air and power cylinder walls to control the flow of the gases through the engine.
It will be readily appreciated that an oscillating cylinder engine that provides complete scavenging or removal of the exhaust gases from the combustion chamber is very advantageous. The engine should allow complete mixing of the air and fuel without the loss of any unburned fuel through the exhaust port. The engine should also be simple, easy to manufacture, lightweight, compact, and require fewer parts than a comparable reciprocating piston engine.